[RFC 3/3] zram: add swap_get_free hint

[Minchan Kim <minchan@kernel.org>]

This patch implement SWAP_GET_FREE handler in zram so that VM can
know how many zram has freeable space.
VM can use it to stop anonymous reclaiming once zram is full.

Signed-off-by: Minchan Kim <minchan@kernel.org>
---
 drivers/block/zram/zram_drv.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 88661d62e46a..8e22b20aa2db 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -951,6 +951,22 @@ static int zram_slot_free_notify(struct block_device *bdev,
 	return 0;
 }
 
+static int zram_get_free_pages(struct block_device *bdev, long *free)
+{
+	struct zram *zram;
+	struct zram_meta *meta;
+
+	zram = bdev->bd_disk->private_data;
+	meta = zram->meta;
+
+	if (!zram->limit_pages)
+		return 1;
+
+	*free = zram->limit_pages - zs_get_total_pages(meta->mem_pool);
+
+	return 0;
+}
+
 static int zram_swap_hint(struct block_device *bdev,
 				unsigned int hint, void *arg)
 {
@@ -958,6 +974,8 @@ static int zram_swap_hint(struct block_device *bdev,
 
 	if (hint == SWAP_SLOT_FREE)
 		ret = zram_slot_free_notify(bdev, (unsigned long)arg);
+	else if (hint == SWAP_GET_FREE)
+		ret = zram_get_free_pages(bdev, arg);
 
 	return ret;
 }
-- 
2.0.0

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